1. Technical Field of the Invention
The object of the invention is a device and a method for cleaning of a filter net of a pulp dryer's fan tower, a pulp dryer's fan tower and a pulp dryer. The invention relates especially to a new manner of arranging vacuum-cleaning at limited areas of a pulp dryer, which are difficult to vacuum-clean, such as at the filter net of a fan tower.
2. Prior Art
A typical pulp dryer of prior art comprises                an actual dryer section in which a pulp web is dried in air flotation drying with hot air jets or the like,        at least one, usually several recirculation fans arranged adjacent to the actual dryer section with which recirculation fans humid air is discharged from the actual dryer section and heated air is blown as drying air into the actual dryer section, and        heating devices with which the discharged humid air is heated before returning it as drying air into the actual dryer section.        
Several fans operating side by side are usually arranged on top of each other in order to create so called fan towers, a necessary amount of which fan towers, in turn, are arranged side by side. The fans are mounted in the fan tower so that their suction openings are confined to the front and back side of the fan tower, seen from the running direction of the web to be dried. Heating devices are arranged on the back and front sides of the fan towers, in front of the blowers' suction openings, which heating devices heat the humid air discharged from the dryer section before the fans.
In front of the heating devices, i.e. on their inlet side there is usually arranged a filter net or the like to prevent shredded paper, fibers, dust or the like from entering the heating device and the blower. Dust sticks to the filter net, which then has to be cleaned every now and then.
Cleaning of the filter nets of a pulp dryer's heating devices, such as steam radiators, nowadays takes place manually with a vacuum-cleaner. The cleaning is performed e.g. once or few times a week. Thus, the person operating the vacuum-cleaner must, at least partly, enter the space between the fan towers, where the temperature is high, even over 100° C., and where the humidity is also high. The vacuum-cleaning is usually performed with a vacuum-cleaning duct connected to the mill's central vacuum system and having a nozzle at its end. The nozzle is moved manually on the surface of the filter net to be vacuum-cleaned. The work is hard, very unpleasant and unergonomic.
Due to the reasons stated above, it is difficult to perform the vacuum-cleaning with sufficient care, and it is therefore not always done often enough. When performing the vacuum-cleaning by hand, it is also difficult to reach well enough for example behind the steam pipes, support elements, beams or the like. Inadequate vacuum-cleaning causes an increase of pressure loss and a reduction in the amount of air in the recirculation fans. This leads, in the dryer section, to an impaired air flotation ability of the pulp web, and to runnability problems. Production is naturally also decreased. Thus, this working phase should be eliminated or it should be made easier to perform.
The Finnish patent publication FI 108882 B describes a pulp dryer's filter net, which is movable in the direction of the inlet side plane of the blast air heating device, and movable to a specific cleaning device, at least partly away from the front of the heating device's inlet side. The solution requires a specific mechanism for moving the filter net.